JOHANNESBURG, South Africa (CNN) -- President Robert Mugabe will win re-election by default if opposition leader Morgan Tsvangirai declines to participate in a runoff, the head of the Zimbabwe Electoral Commission told CNN on Thursday.
Morgan Tsvangirai has argued that a run-off is unnecessary and that the government would rig the outcome.
His remarks come a day after a senior official in Mugabe's ruling ZANU-PF party said the two candidates must compete in a run-off based on election results in the party's hands.
The government has not released results from the March 29 presidential election, and reports of violence against opposition supporters have swirled in Zimbabwe amid heightened tensions since then.
Tsvangirai says he won the election with 50.3 percent of the vote -- just more than the 50 percent plus one vote that a candidate needs to win.
His opposition party, the Movement for Democratic Change (MDC), has argued that a runoff is unnecessary and that the government would rig the outcome.
If Tsvangirai does not participate in a runoff, Mugabe would retain the presidency, according to George Chiweshe, head of the Zimbabwe Electoral Commission.
On Wednesday, a senior official in Mugabe's ruling ZANU-PF party said that Tsvangirai received 47 percent of the vote in last month's election, compared with 43 percent for Mugabe. The official did not want to be named.
Asked if the results came from the Zimbabwe Electoral Commission (ZEC), the official would not specify.
"We have ways of knowing these things," he said.
As expected, a spokesman for Tsvangirai's Movement for Democratic Change rejected ZANU-PF's results as rigged and said the party would refuse to participate in any run-off vote.
"ZANU-PF is trying to position a discussion about a run-off where there is no run-off," Tsvangirai's spokesman, George Sibotshiwe, told CNN. "Mugabe must concede defeat."
MDC maintains that, according to its count, Tsvangirai won 50.3 percent of the vote. It has repeatedly vowed not to accept a result other than an outright victory for Tsvangirai.
Zimbabwean Information Minister Sikhanyiso Ndlovu would not confirm the official's data, telling CNN that the Zimbabwe Electoral Commission has not yet released its official results.
The commission's head, Chiweshe, said the ZEC will submit the results of the March 29 presidential race to the ruling and opposition parties on Thursday to begin the verification process.
That is the final step before making the results public, which Zimbabwe has been under intense international pressure to do.
Mugabe's ZANU-PF ruling party and Tsvangirai's MDC will compare the results they have tallied from polling stations with the final ZEC count, Chiweshe said.
Independent candidate Simba Makoni will also participate in the process.
Once all parties are satisfied, they will sign verification forms and the results can be released, Chiweshe said.
It is highly unlikely that MDC and ZANU-PF will agree on the results, but Chiweshe said ZEC can publicly announce its results in the event of a stalemate. He did not say when that would happen.
There has been widespread violence and accusations from the opposition that and his supporters have orchestrated a plan to remain in control of government and weed out opposition supporters by general intimidation.
Tendai Biti, secretary-general of the MDC, told CNN that the Security Council must take action.
"If the U.N. fails Zimbabwe, then the U.N. is failing itself, failing the spirit of the founding fathers." he said.
U.S. President Bush repeated his position on Tuesday that the opposition won Zimbabwe's March 29 election.
"The will of the people needs to be respected in Zimbabwe," Bush said. "And it is clear that they voted for change, as they should have, because ... Mr. Mugabe has failed the country." E-mail to a friend